1. Field of the Invention
The present invention relates to a steering system for vehicles, and more particularly to a steering system in which both the front wheels and the rear wheels are steerable in response to steering rotation of the steering wheel.
2. Description of Relevant Art
In conventional steering systems for vehicles, generally only the front wheels are steered by operating the steering wheel. However, there has already been proposed a novel steering system in which both the front wheels and the rear wheels are steered by operating the steering wheel (see U.S. patent application Ser. Nos. 107,717 and 107,718 both filed Dec. 28, 1979 in the name of the present applicant, and now U.S. Pat. Nos. 4,313,514 and 4,295,657, respectively). In such novel steering system, the front wheels and rear wheels are both steered in the same direction within a relatively small steering angle range of the steering wheel and, on the other hand, for a relatively large steering angle range the rear wheels are steered in the opposite direction relative to the front wheels.
With the novel steering system as described hereinabove, various advantages have been attained. For example, the cornering forces causing yawing around the center of gravity of a vehicle are generated at the front wheels and rear wheels without delay therebetween, thus resulting in an improved response of the rear wheels. In addition, the direction of the vehicle substantially coincides with the tangential line of turning loci when the vehicle is turned, thus ensuring (together with the foregoing advantage) improved drivability with a ready grasp of the feeling necessary for steering. Further, the minimum turning radius of the vehicle can be remarkably reduced.
From a practical standpoint, it is desired that the novel steering system of the aforesaid type have a structure in which the steering angle of the rear wheels is selective with respect to the steering angle of the steering wheel or the steering angle of the front wheels, because a possible free selection of a steering angle ratio between the steering wheel or front wheels and rear wheels may provide improved practical operation. Moreover, when taking into consideration the fact that relatively large steering angles of the steering wheel are experienced mainly at low driving speeds, such as when the vehicle is being driven into a garage, is approaching a road side, and/or is starting from a road side where it has been parked, it is advantageous for a certain type of vehicle to have, in a relatively large steering angle range of the steering wheel, only the front wheels steered, without the rear wheels being steered in the opposite direction relative to the front wheels, i.e., holding the steering angle of the rear wheels at or in the vicinity of zero degrees. If the system fulfills such a requirement for the steering of the rear wheels, further preferable results would thus be attainable.